The invention relates to a method and device for the manufacture of cutting elements comprising diamond material bound in a metal matrix mass, in particular, for deep drill bits the method involving the hot pressing of a base powder mixture inserted into a recess of a mold block and hermetically enclosed in a high pressure furnace.
With the manufacture of cutting elements which comprise diamond material bound in a metal matrix mass, a close binding of the diamond material to the matrix mass, which serves as carrier, is desired. This binding is supposed to ensure that the diamond material remains in its carrier, even under the influence of shock-like shearing stress, which occurs during the cutting action. Basically, a binding between two materials can be attained by a diffusion process occurring at increased temperature, whereby a reciprocal penetration of the substances takes place in a peripheral area and thus produces a bonding zone. Since, however, diamond is unstable under atmospheric pressure at temperatures of this type, an increase of pressure must take place in addition to the temperature increase for a successful carrying out of the diffusion process.
From U.S. Pat. No. 3,745,623, a method for the manufacturing of cutting elements by means of hot pressing is already known. Here, a base powder mixture is, first of all, inserted into a recess, which is provided with a metal lining, of a mold block, the opening is then sealed with a cover sheet and a crown piece made of the same material is placed onto the mold block. This arrangement is inserted, if necessary, in a cascade manner into a high pressure furnace, and there sintered at increased temperature and increased pressure, whereby the pressure is applied in only one directional component. After cooling and lowering of the pressure, the cutting elements can be removed from the recesses of the mold blocks.
It was shown that the metal lining serving as hermetic seal for the base powder mixture during the sintering process allows only a relatively simple geometric shaping of the recesses, if it is not to be damaged due to extreme strain paths, when being placed against the walls of the recesses. In addition, a directed pressure increase during the sintering process leads, after cooling, to strains inside the cutting elements, which could bring about a premature destruction with subsequent shearing load.